Gas sensing using xerogel coated whispering gallery mode resonators

To efficiently sense small gas concentrations using a whispering gallery mode resonator a xerogel coating can be applied onto the surface of the resonator. In this way, gas molecules can enter into the xerogel layer where they can interact with the electric filed of the whispering gallery modes. Here we present some results on ammonia gas detection using a silica microsphere coated with a sol-gel porous silica xerogel. The frequency shift of an isolated whispering gallery mode was measured in dependence on the ammonia gas concentration in the testing chamber and efficient gas sensing was observed. We discuss the observed results and elaborate how the proposed systems sensitivity can be tailored in respect to the geometrical parameters of the system including the sphere radius and the coating thickness.